1. Field of the Invention
The present application relates to a method for manufacturing a resin-framed membrane electrode assembly for a fuel cell.
2. Discussion of the Background
In general, solid polymer electrolyte fuel cells use solid polymer electrolyte membranes formed of polymer ion exchange membranes. According to this type of fuel cells, a membrane electrode assembly (hereinafter also referred to as MEA) including a solid polymer electrolyte membrane sandwiched between an anode and a cathode is held between separators (bipolar plates), each of the anode and the cathode including a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon). A predetermined number of such fuel cells are stacked to constitute a fuel cell stack which is used as an onboard fuel cell stack.
The MEA of this type is sometimes designed as a step-type MEA in which one of the electrode layers is designed to have a surface area smaller than that of the solid polymer electrolyte membrane and the other electrode layer is designed to have a surface area equal to that of the solid polymer electrolyte membrane. In such a case, framed MEAs equipped with resin frame members are used to reduce the amount of relatively expensive solid polymer electrolyte membranes and to protect the solid polymer electrolyte membranes which are thin and have low strength.
For example, referring to FIG. 7, Japanese Unexamined Patent Application Publication No. 2008-41337 discloses a membrane electrode assembly (MEA 6) that includes a polymer electrolyte membrane 1, a first electrode layer 2 on one of the surfaces of the polymer electrolyte membrane 1, and a first gas diffusion on a surface of the first electrode layer 2 opposite to the polymer electrolyte membrane 1.
The MEA 6 further includes a second electrode layer 4 on the other surface of the polymer electrolyte membrane 1, and a second gas diffusion layer 5 on a surface of the second electrode layer 4 opposite to the polymer electrolyte membrane 1.
The MEA 6 is fitted in a resin frame 7 that surrounds the entire outer peripheral end of the polymer electrolyte membrane 1 and at least the part of the outer peripheral end of the first gas diffusion layer 3 and the second gas diffusion layer 5 so as to cover the side of the electrolyte membrane 1.
The first gas diffusion layer 3 and the first electrode layer 2 are arranged so that the entire outer peripheral end of the first gas diffusion layer 3 is within the outer peripheral end of the polymer electrolyte membrane 1 and that a surface region of the polymer electrolyte membrane 1 remains in a region between the outer peripheral end of the polymer electrolyte membrane 1 and the outer peripheral end of the first electrode layer 2 so that surrounds the entire outer peripheral end of the first electrode layer 2. The second gas diffusion layer 5 extends to at least part of the surface opposite to the surface region over the entire outer peripheral end of the electrolyte. The resin frame 7 is fixed to at least part of the surface region.